1. Field of the Invention
This invention relates to a light irradiating apparatus for use when an image display element is to be uniformly illuminated, and more particularly to an image displaying apparatus such as a liquid crystal projector using such light irradiating apparatus in an illuminating system.
2. Related Background Art
In a liquid crystal projector for enlarging and projecting an image displayed on a liquid crystal display element, use has heretofore been made of an illuminating system for condensing a light emitted from a white light source in a particular direction by a reflecting mirror, and uniformly illuminating the liquid crystal image display element by a fly-eye lens integrator. In this illuminating system, as proposed in Japanese Laid-Open Patent Application No. 8-304739, etc., use is made of a polarization converting element for aligning the direction of polarization of the illuminating light in accordance with the polarization characteristic of the liquid crystal display element.
FIG. 12 of the accompanying drawings shows the illuminating system (polarization converting system) proposed by the above-mentioned publication. As shown in this figure, when two fly-eye lens 101 and 102 and a polarization converting element 103 are to be combined together, the separation of polarization is such that non-polarized illuminating light is separated into P-polarized component and S-polarized component at the condensing position of the first fly-eye lens 101 formed near the second fly-eye lens 102. That is, only the light transmitted through the area Fa of a half of the pitch of each lens constituting the second fly-eye lens 102 is polarization-converted.
In the construction as shown in FIG. 12, however, there is the problem that when the parallelism of the illuminating light incident on the first fly-eye lens 101 is bad (the illuminating angle .alpha. is great), the condensed spot (point image) by the first fly-eye lens 101 becomes large and therefore, the light protrudes out of the range of the area Fa and the percentage of the quantity of light which can be used for polarization conversion is reduced. When use is made of a construction as proposed, for example, in Japanese Laid-Open Patent Application No. 10-133198 wherein an elliptical mirror and a concave lens are combined and illuminating light is compressed into a narrower area, action similar to that of a teleconverter comprising positive and negative lenses is provided by the positive power of the elliptical shape and the negative power of the concave lens, and in contrast with a construction for collecting light by a parabolic mirror, conversion is effected so that the parallelism of the illuminating light emerging from the concave lens may be aggravated (the illuminating angle may increase). Therefore, even if the polarization converting element proposed in Japanese Laid-Open Patent Application No. 8-304739 is used in it, the rate of the light transmitted through the area Fa of a half of the lens pitch of the second fly-eye lens is reduced and thus, a desired increase in the quantity of light cannot be expected.
Also, even when as proposed in Japanese Laid-Open Patent Application No. 10-133141, an elliptical mirror and a concave lens are combined and a polarization converting element is provided between fly-eye lenses, an area for aligning the direction of polarization (an area through which the light of P-polarized component is transmitted and an area through which the light of S-polarized component is transmitted) is provided near the second fly-eye lens correspondingly to the area of a half of the lens pitch of the second fly-eye lens and therefore likewise, a reduction in the percentage of the polarization-converted light occurs.